N-Carboxyethyl chitosan was synthesized according to the
method reported by us earlier [28]. Briefly, 4.0 g of chitosan (corresponding
to 17 mmol NH2) was dissolved in 250 mL of water
containing 7.7 mL acrylic acid at 50 ◦C under constant stirring for
2 day. After that, 1 N aqueous NaOH was added to the reaction
mixture to adjust the pH to 10–12 in order to convert the carboxylic
acid to its sodium salt. The mixture was precipitated by
acetone and then dialyzed (membrane molecular weight cutoff
12,000
×
g mol−1) against water for 2 days and lyophilized to obtain
pure CECS. 1H NMR spectrum was recorded on a Bruker AV 400
NMR instrument.